Jeff Sessions had been a four-term U.S. senator, had served as the top Republican on important committees and had a strong following among hardcore conservatives. Then he went to work for the Trump administration. Now he is publicly ridiculed and mocked — by President Trump.

In his latest tweet disparaging his own attorney general, Trump lastthis week called Sessions’s conduct at Justice “DISGRACEFUL!” and he has privately referred to Sessions as “Mr. Magoo.”

Ben Carson had been a brilliant brain surgeon before mounting a surprisingly strong run for the Republican presidential nomination. Then he went to work for the Trump administration as secretary of housing and urban development. Now he’s the punchline for jokes about government waste.

Under public ridicule, Carson said lastthis week he would cancel a $31,561 order for a dining-room set for his office. He also has defied staff warnings that he is violating ethics rules by allowing his son to arrange an event for HUD that could benefit his son’s business.

Jared Kushner, the president’s son-in-law, was put in charge of Middle East peace, government reform, the opioid crisis, criminal-justice reform, and relations with Mexico, China and the Muslim community.

Now he has lost his security clearance and is a poster boy for conflicts of interest. The New York Times reportedlastthis week that the Kushner family’s struggling real estate business was lent hundreds of millions of dollars by companies whose executives met with Kushner at the White House. This came after The Post reported on foreign intercepts showing that four countries believed they could influence Kushner because of the family company’s debt.

And all this developed over one week — a week in which White House communications director Hope Hicks resigned after answering lawmakers’ questions in the Russia probe. Trump must now designate a communications director for the seventh time since his election. Turnover among White House senior staff has reached a record 40 percent, according to an ongoing tally by Kathryn Dunn Tenpas of the Brookings Institution. Among the 12 most senior staff positions, seven have departed.

It’s a peculiar phenomenon: Trump bumbles along, his approval rating low but relatively constant, while those he touches are disgraced or ruined. Trump delights in destroying foes, but his indiscriminate destruction brings down friends just as easily.

Why? To start, Trump didn’t have his choice of first-tier talent. Most of those with governmental experience and policy credentials wanted nothing to do with Trump, who in any case disdained the party elites. So he wound up with White House official Omarosa Manigault, whose prior experience involved being a contestant on Trump’s reality show; and Hicks, who was a model and adviser on Ivanka Trump’s fashion line before making her political debut with the Trump campaign; and Sebastian Gorka, a former Breitbart News figure claimed by a Hungarian neo-Nazi group as a member; and poorly vetted figures such as Rob Porter (wife-beating allegations), Paul Manafort (indictment) or Rick Gates (guilty plea).

There is also the anything-goes atmosphere Trump created by ignoring conflict-of-interest standards. The president is exempt from such rules, but his appointees, following his lead, have wound up in trouble. Price, a well-regarded Republican lawmaker, was forced to quit as health and human services secretary after being hung out to dry by Trump over Price’s excessive use of private jets. Other Cabinet members have had similar dust-ups: Mnuchin requested a government jet to take him and his wife on their European honeymoon.

Even those who entered with solid credentials — Spicer, Tillerson, Priebus, Shulkin, John F. Kelly, Rod J. Rosenstein, Katie Walsh — have seen their reputations soiled by Trump, whose loyalty code is unidirectional and whose chaotic leadership drives people to the exits.

Consider the cautionary tale of Gary Cohn, Goldman Sachs president before coming to Trump’s White House. He first endured the humiliation of standing at Trump’s side when Trump defended the white supremacists in Charlottesville, then after criticizing Trump’s behavior was passed over for an appointment to the Fed, and now has lost a fight to keep Trump from imposing steel tariffs.